Fault-tolerant fuel isolation from engine firebay

ABSTRACT

Fuel isolation systems, apparatuses and methods are described. In some embodiments, a system comprises a fuel tank, a fuel pump, an engine, a firewall, a fuel line from the fuel tank to the engine, a connector coupled inline with the fuel line on a cold side of the fuel line, a normally closed valve coupled to the connector, an air feed line coupled to an ullage of the fuel tank and to the valve. In the event of an engine fire condition, a control unit outputs signaling to turn off the fuel pump and open the valve to introduce air from the ullage into the fuel line. The introduced air provides a siphon break in the fuel line such that the fuel cannot be siphoned and the only fuel that can pass the firewall is the remaining fuel in the fuel line downstream of the connector and the introduced air.

TECHNICAL FIELD

This invention relates generally to fuel delivery systems in aircraft,and more specifically to systems for isolating fuel from an aircraftfirebay.

BACKGROUND

Numerous international codes and regulations cover various aspects ofaircraft. For example, to be compliant with the European Aviation SafetyAgency Certification Specification, (EASA) CS 23.1189, and the UnitesStated Code of Federation Regulations, 14 CFR 23.2440(d)(1), aircraftmust include a means to shut-off or prevent hazardous quantities offlammable fluids from flowing into, within or through any enginecompartment in the event of an engine fire. Accordingly, in the event ofan engine fire, the flow of fuel to the engine must be able to be shutoff. Traditional approaches involve the use of a normally open shut offvalve in line with the fuel feed line on the cold side of the firewall,the engine being located in the firebay on the hot side of the firewall.In the event of an engine fire, the shut off valve is closed which cutsoff the flow of fuel from the point of the valve to the engine. Thissolution is effective; however, introduces a single point of failure inthe safety system. That is, due to electrical and/or mechanical issue/s,the normally open shut off valve may erroneously close when there is notan engine fire or other event. In this event, the engine will notreceive further fuel and propulsion is lost. Such an event can becatastrophic in single engine aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Disclosed herein are embodiments of systems, apparatuses and methods forisolating fuel from an engine firebay. This description includesdrawings, wherein:

FIG. 1 comprises a simplified diagram of a conventional system forisolating fuel from the firebay of an aircraft;

FIG. 2 comprises a simplified diagram of a system for isolating fuelfrom the firebay of an aircraft according to some embodiments;

FIG. 3 comprises a functional block diagram of a conventional system forisolating fuel from the engine firebay;

FIG. 4 comprises a functional block diagram of a system for isolatingfuel from the firebay of an aircraft according to some embodiments;

FIG. 5 comprises a diagram of a system for isolating fuel from thefirebay of an aircraft according to some embodiments;

FIG. 6 comprises a flow diagram illustrating a process for isolatingfuel from the firebay of an aircraft according to some embodiments;

FIG. 7 comprises a flow diagram illustrating a process for restartingoperation after fuel has been isolated from the aircraft firebayaccording to some embodiments; and

FIG. 8 comprises a functional block diagram of a control unit inaccordance with some embodiments.

Elements in the figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale. For example, the dimensionsand/or relative positioning of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of various embodiments of the present invention. Also,common but well-understood elements that are useful or necessary in acommercially feasible embodiment are often not depicted in order tofacilitate a less obstructed view of these various embodiments of thepresent invention. Certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. The terms and expressions used herein have theordinary technical meaning as is accorded to such terms and expressionsby persons skilled in the technical field as set forth above exceptwhere different specific meanings have otherwise been set forth herein.

DETAILED DESCRIPTION

Generally speaking, pursuant to various embodiments, systems,apparatuses and methods are provided herein for isolating fuel from anengine firebay. Several embodiments described herein provide a solutionthat will isolate fuel from the firebay compliant with known regulationsand that will also not introduce a single point of failure in the safetysystem.

Generally, according to some embodiments, fuel isolation to the enginefirebay is provided through the use of a valve on the cold side of afirewall, the valve being coupled between an ullage of a fuel tank andan elevation of the fuel feed line at or above the ullage of the fueltank. In the event of an engine fire condition, the airframe fuel pumpsare turned off and the valve is opened to introduce air from the ullageportion into the fuel feed line as a vacuum break or siphon break suchthat the only fuel that will pass the firewall is the remaining fuel inthe line downstream of the introduced air, and additional fuel cannot besiphoned. In some embodiments, to ensure adequate ullage and to reducesystem pressure, a jettison valve is briefly opened and closed. In someembodiments, the valve replaces a conventional latching solenoidcontrolled shut valve at the firewall. In some embodiments, the valvedoes not introduce a single point of failure in the system such thatpropulsion system reliability is not sacrificed. For example, if thevalve erroneously at least partially opens during normal operation dueto a failure, a small amount of fuel may flow through the valve and backinto the fuel tank, but fuel will continue to flow through the fuel feedline to the engine at a sufficient level for safe operation of theengine. In some embodiments, in the event a fire condition that resultsin operation of the valve but the event is actually not a fire event,the valve is closed and the airframe fuel pumps and engine are turnedback on to resume normal operation. In some embodiments, the operationof the valve is initiated by the pilot or automatically by a controlunit. In some embodiments, the aircraft is a manned aerial vehicle or anunmanned aerial vehicle. In some embodiments, the aircraft is amulti-engine or single engine aircraft. In alternative embodiments, thesystem and method are used in the same manner in other than aerialvehicles, such as watercraft (e.g., surface boat or submarine vehicles)and ground vehicles (e.g., automobiles, trucks).

In some embodiments, a system and method for use in isolating fuel froman aircraft firebay comprises: a fuel tank; an airframe fuel pump; anengine located within the aircraft firebay; a firewall separating theaircraft firebay from a volume containing the fuel tank and the airframefuel pump; a fuel feed line extending from the fuel tank to the airframefuel pump and through the firewall to the engine, the fuel feed linefluidly connecting the fuel tank to the engine and additional aircraftsystems, wherein the airframe fuel pump is configured to pump fuel fromthe fuel tank through the fuel feed line to the engine, wherein the fuelfeed line comprises a cold side portion extending from the fuel tank tothe firewall and a hot side portion extending from the firewall to theengine; a connector coupled inline with the fuel feed line at a locationof the cold side portion of the fuel feed line; a valve coupled to theconnector, the valve configured in a normally closed orientation; an airfeed line coupled to an ullage portion of the fuel tank and to thevalve; and a control unit configured to control operation of at leastthe airframe fuel pump and the valve. In the event of an engine fire,the control unit is configured to output control signaling to: turn offthe airframe fuel pump to stop pumping the fuel through the fuel feedline; and open the valve to introduce air from the ullage portion of thefuel tank into the fuel feed line, wherein the air introduced by thevalve provides a siphon break in the fuel line such that the fuel cannotbe siphoned and the only fuel that can pass the firewall is theremaining fuel in the fuel feed line downstream of the connector and theintroduced air.

Referring now to FIG. 1, a simplified diagram is shown of a conventionalsystem for isolating fuel from the firebay of an aircraft. Shown is afuel system including a fuel tank 102, a fuel feed line 104, airframefuel pump/s 106 (also referred to as fuel pump 106), a shut off valve108, a firewall 110, an engine 112, a control unit 113 and sensors 116.Fuel is stored in the fuel tank 102 under pressure. Fuel is pumped fromthe fuel tank 102 by the fuel pump 106 via the fuel feed line 104through the open shut off valve 108 through the firewall 110 and to theengine 112. It is understood that many system components are notillustrated. The control unit 113 is electrically coupled to and outputsvarious control signals to the fuel pump 106, the shut off valve 108 andthe engine 112. The sensors 116 are located proximate to the engine 112and are used to sense or detect conditions indicating an engine fire.The sensors 116 output signals to the control unit 114. The portion ofthe fuel feed line 104 upstream of the firewall (between the fuel tank102 and the firewall 110) can be referred to as the cold side portion104 a of the fuel feed line 104, and the portion of the fuel feed line104 downstream of the firewall (between the firewall 110 and the engine112) can be referred to as the hot side portion 104 b of the fuel feedline 104. The volume on the hot side portion 104 b containing the engine112 is the firebay 118.

In operation, under control of the control unit 113, fuel is pumped fromthe fuel tank 102 via the fuel feed line 104 through the firewall 110 tothe engine 112 by the fuel pump 106. It is understood that there areadditional components that are not shown at the fuel pump 106 includingfuel filters and heat exchangers and fuel can be sent to other fuelbays, e.g., by a jet pump manifold. In this diagram, when the sensors116 detect significant heat or other condition indicative of an enginefire, the sensors 116 output a signal to the control unit 113. On pilotcommand, the control unit 113 attempts to shut down the engine 112,turns off the fuel pumps 106 and causes the shut off valve 108 to close.This stops the flow of fuel to the engine 112 and meets many of thevarious aviation codes. The shut off valve 108 is a solenoid activatedlatching valve that when closed does not require further power to remainclosed, and will remain closed for the remaining duration of flight.However, such systems leads to a single point of failure. That is, it ispossible that the shut off valve 108 may erroneously close or partiallyclose due to a mechanical and/or electrical failure. In that case,despite the fact that there is not an engine fire and the fuel pump 106is in normal operation, no fuel will reach the engine and propulsionwill be lost. Additionally, should the sensors 116 indicate an enginefire and shutdown is initiated, but the event is not actually an enginefire, the shut off valve 108 cannot be re-opened during flight. Ineither case, propulsion is lost. Such situations can be catastrophic insingle engine aircraft.

Referring now to FIG. 2, a simplified diagram is shown of a system forisolating fuel from the firebay of an aircraft according to someembodiments. In addition to the components already identified in FIG. 1,shown are a valve 202, a connector 208, and an ullage portion 204 and afuel portion 206 of the fuel tank 102, and an air line 210. In someembodiments, instead of including a shut off valve 108 in the fuel feedline at or upstream of the firewall 110, the valve 202 is fluidlyconnected between the ullage portion 204 of the fuel tank 102 and thefuel feed line 104 at the connector 208. That is, the air line 210 isconnected from the ullage portion 204 to the fuel feed line 104 by thevalve 202 and the connector 208. The connector 208 is coupled to thefuel feed line 104 at an elevation point of the fuel feed line that isat or above a level corresponding to a low level of the ullage portion204 of the fuel tank 102. In the illustrated embodiment of FIG. 2, theconnector 208 is at the high elevation point A of the fuel feed line104. In the illustrated embodiment, the low elevation point of theullage portion 204 is illustrated at line B. Thus, in some embodiments,the connector 208 is coupled to the fuel feed line 104 at an elevationat or above line B. In some embodiments, the connector 208 is a teeconnector coupled inline with fuel feed line 104 and is connected to thevalve 202. In some embodiments, the valve 202 is a non-latching,solenoid activated valve in a normally closed orientation that iselectrically operated. In order to open the valve 202, a control signal(e.g., a 28 volt signal) is output by the control unit 114 which causesthe valve to open for the duration of the application of the controlsignal. In some embodiments, the contents of the fuel tank 102 aremaintained under pressure. That is, the ullage portion 204 includes airunder pressure. In other embodiments, the air in the ullage portion isnot under pressure, e.g., when the fuel tank is low and/or when thejettison system is activated. It is noted that the control unit 114 issimilar to the control unit 113 but includes programming andfunctionality to implement fuel isolation methods in accordance withseveral embodiments.

When the sensors 116 output signals indicating an engine fire and thefuel isolation protocol is initiated (either automatically by thecontrol unit 114 or after signal from the pilot), the control unit 114outputs signaling to attempt to turn off the engine, to remove power tothe fuel pumps 106 and to open the valve 202. When the valve 202 opens,air from the ullage portion 204 is introduced into the fuel feed line104 at the connector 208, e.g., an air bubble is introduced into thefuel feed line 104. The introduced air provides a vacuum break or siphonbreak in the fuel feed line 104 at point A that will prevent siphonaction in the fuel feed line 104. In this situation, fuel is not pumpedthrough the fuel feed line 104 by the fuel pumps 106 and due to theintroduction of the air, the engine 112 (or ruptured lines in thefirebay 118) may not siphon fuel through the fuel feed line 104 to theengine 112. And thus, the only fuel that can pass the firewall 110 isthe remaining fuel in the fuel feed line 104 downstream of theintroduced air, i.e., any fuel already in the fuel feed line 104 betweenpoints A and C. The distance between A and C is designed such that thevolume of fuel that can pass the firewall 110 is minimal and, in anyevent, less than the amount allowed by various international codes andregulations. In some embodiments, the volume of fuel between points Aand C is less than one liter; thus meeting aviation codes andregulations that indicate a hazardous amount of fuel cannot enter theenter, and defining a hazardous amount as 1 liter. In some embodiments,the valve 202 is referred to as an anti-siphon valve since in thisconfiguration and use, it functions to break siphon action in the fuelfeed line 104 to prevent fuel from being siphoned through the fuel feedline 104; however, the valve 202 itself is not a traditional anti-siphonvalve used to prevent fluid flow from reversing as is understood in theart. In some embodiments, the valve is a simple, non-latching, solenoidactivated valve in a normally closed orientation. It is understood thatthe valve 202 and connector 208 may be integrated into one device or maybe separate devices coupled or connected together. The air line 210connects to the ullage portion 204 to provide the source of air forintroduction into the fuel feed line 104. It is understood that thevalve 202 is connected to the ullage portion 204 by a conduit, hose orpiping line and connector at the fuel tank (not shown).

In some embodiments, a jettison valve (not shown in FIG. 2, see alsoFIG. 4) is briefly opened at the same time or shortly after the valve202 is opened. Normally, as is well known, the jettison valve is used todump large volumes of fuel from the fuel tank/s. In this use, thejettison valve is opened for a short period of time (e.g., 15 seconds)in order to ensure that there is adequate ullage available and to reducepressure in the fuel system.

In some embodiments, the control unit 114 also causes the propeller/s ofthe aircraft to be feathered in order to provide the lowest drag andgive the aircraft the best glide performance given that there is anengine fire event and that the engine is being shut down. Furtherdetails of such embodiments are described in more detail in thediscussion below corresponding to FIG. 4.

In some embodiments, in the illustrated configuration, the fuelisolation to the firebay 118 is reversible in the event it is determinedthat the event is not an actual engine fire. In such event, the controlunit 114 outputs signals to turn on the fuel pump 106 and close thevalve 202, unfeather the propeller/s, and then turn back on the engine112. In this case, the flow of fuel will resume to the engine. Theengine will experience a brief loss of power as it ingests the airintroduced into the fuel feed line 104 and then will resume normaloperation.

In some embodiments, the fuel isolation system and method does notintroduce a single point of failure in the system, as does a traditionalshut off valve 108. If the valve 202 erroneously partially or fullyopens due to an electrical and/or mechanical failure, a small portion ofthe flowing fuel may pass through the valve 202 and reenter the fueltank 102, but the majority of the fuel will continue flowing through thefuel feed line 104 through the firewall 110 to the engine 112. In anyevent, a sufficient amount of fuel will continue to flow to the engine112 to provide safe operation of the engine. In some embodiments, thisis due to the size differential between the valve 202 and air line 210connecting the valve 202 to the fuel tank 102, and the fuel feed line.For example, in some embodiments, the diameter of the air line 210connecting the ullage portion 204 to the valve 202 is about 0.25 inches(0.0635 cm) whereas the diameter of the fuel feed line 104 is about 1.0inches (2.54 cm). In other words, the ratio of the diameter of the airline 210 to the fuel feed line 104 is about 1:4. It is understood thatthis ratio may be different and depends on the dimensions, pressures,flow rates, volumes and other characteristics of the particular system.For example, the size ratio may be between 1:2, 1:3, 1:4, 1:5 and so on.As can be seen in this embodiment, should the valve 202 open due to afailure, safe operation of the aircraft continues.

Referring next to FIGS. 3 and 4, are functional block diagrams of aconventional system for isolating fuel from the engine firebay (FIG. 3),and a system for isolating fuel from the firebay of an aircraftaccording to some embodiments (FIG. 4), respectively. The diagrams ofFIGS. 3 and 4 provide additional details relative to the diagrams ofFIGS. 1 and 2.

In a conventional aircraft, the fuel tank system can include multiplefeed tanks 302 and a header fuel tank 304. For example, feed tanks 302may be located in the aircraft wings that store and feed fuel to theheader fuel tank 304. Feed tanks 302 may be selected to supply fuel tothe header fuel tank 304. The header fuel tank 304 is fluidly coupled tothe airframe fuel pumps 106 which are connected to the fuel filter 306and a jet pump manifold 308. The jet pump manifold 308 directs fuel tothe selected feed tank 302 and the fuel feed line 104. As describedabove, the fuel feed line 104 passes through the shut off valve 108 andthe firewall 110 to the engine 112. A return manifold 310 is fluidlycoupled to the header fuel tank 304 and directs excess fuel back to thefeed tank/s 302 and to a jettison valve 312. The jettison valve 312 canbe opened to jettison fuel from the header fuel tank 304. A vent box 314is fluidly coupled to the selected feed tank/s 302 to allow air from theenvironment in to replace fuel that is consumed. Fuel cannot exit thevent box 314. It is noted that when referring to two components beingfluidly coupled or connected, it is understood that the appropriateconduit, hose or pipe structure/s and connector/s are provided toconnect the two components such that fluid (air and/or liquid asappropriate) can flow between the components. There may be one or moreconduit, hose or pipe structures and one or more connectors and/orcouplers coupling the structures and connecting to the elements.

In FIG. 3, the control unit 113 is at least electrically coupled to andcontrols the fuel pumps 106, the engine 112, the jettison valve 312, andthe shut off valve 108. As illustrated, the sensors 116 are implementedas a sensor array (e.g., duplex fire sensor array) that extends aboutthe engine 112. In the event the sensors 116 detects conditionsindicating an engine fire, the sensors 116 output an electrical firesensor signal 317 to the control unit 113. In some systems, the pilot318 is informed of the sensor condition and allowed to determine if theevent is an engine fire. That is, it is possible that the sensor arraywill detect an engine fire condition, but there is not actually anengine fire. It is the decision of the pilot 318 to initiate fuelisolation, and this initiation signal is sent to the control unit 113.When fuel isolation is initiated, the control unit 113 outputs theelectrical signal to the shut off valve 108 causing it to close andeliminating fuel flowing through the firewall.

Referring to FIG. 4, similar to that shown in FIG. 2, in someembodiments, the shut off valve in the fuel feed line at or upstream ofthe firewall 110 is not included and the mechanism such as described inconnection with FIG. 2 is used. In these embodiments, the valve 202fluidly couples the air line 210 from the ullage portion of the headerfuel tank 304 to the connector 208 at an elevation at or above anelevation corresponding to a low elevation level of the ullage portion.In some embodiments, the connector 208 is located at the high elevationpoint in the fuel feed line 104. In some embodiments, the sensor array402 is implemented as rope style sensor that is string around thefirebay. The rope line includes an internal tube filled with a gas thatexpands when exposed to heat. When there is an engine fire condition,the gas expands and closes a pressure switch, which provides or outputsthe sensor signal 317 to the control unit 114, the control unit 114receiving the sensor signal 317. In some embodiments, there aremultiple, redundant rope style sensor arrays 402 strung about differentportions of the firebay. This can allow multiple sensor readings, andthe pilot 318 or control unit 114 can use these signals and compare themin determining whether to initiate fuel isolation. When the sensors 402detect a condition indicative of an engine fire, the signal 317 is sentto the control unit 114. Once fuel isolation is instructed by the pilot318, the control unit 114 outputs the signals to turn off the engine112, turn off the airframe fuel pumps 106 and open the valve 202. It isnoted that in some embodiments, the fuel pump 106 is a positivedisplacement pump with an internal bypass. As described above, thiscause air from the ullage portion of the header fuel tank 310 to flowthrough the air line 210 and be introduced into the fuel feed line 104at the connector 208. No fuel is being pumped by the fuel pumps 106 andthe air introduced into the fuel feed line 104 provides a siphon breaksuch that fuel cannot be siphoned by the engine 112, by ruptured linesin the firebay, or siphoned by any other action. The only fuel that canflow past the firewall 110 is the remaining fuel in the line 104 fromthe connector 208 (point A) to the firewall 110 (point C). It is notedthat the control unit 114 includes the control circuitry to control andoperate the system, one or more memories and one or more interfacedevices. The control circuitry can include one or more processors.Control code resides in the control unit and is executed by the controlcircuitry to control the fuel system.

In some embodiments, the jettison valve 312 may also be briefly openedand closed to ensure adequate ullage and/or to reduce pressure in thefuel system. That is, the control unit 114 can also output a signal tothe jettison valve 312 to cause it to open. In some embodiments, thejettison valve 312 is an electrically controlled, latching solenoidactivated valve. The operation of the jettison valve 312 is not for thetraditional purpose of the jettison valve to dump a volume of fuel,e.g., to reduce weight. The jettison valve 312 is blipped, i.e., openedfor a short duration, then closed. The duration that the jettison valve312 is held open may be dependent on the characteristics of the specificsystem but in some embodiments, may be between about 5 and 30 seconds,between about 10 and 20 seconds. In some embodiments, the jettison valve312 is opened for about 15 seconds. The use of the jettison valve 312 isoptional in some embodiments. That is, some fuel systems may not need toopen the jettison valve 312.

In some embodiments, when initiating fuel isolation, the control unit114 also outputs a control signal to the propeller controller 404 tooutput signaling to the propeller/s 406 to feather the propeller/s 406.Feathering the propellers 406 provides the lowest drag and gives theaircraft the best glide performance given that there is an engine fireevent and that the engine 112 is being shut down.

In some embodiments, as described above, the fuel isolation process isinitiated by the pilot 318 based on being informed that the sensors 402have detected a condition indicative of an engine fire. In someembodiments, the pilot 318 is an onboard pilot in the aircraft andcontrolling flight of the aircraft. In some embodiments, the pilot isremote and pilots the aircraft from a ground station or other airstation, such that the aircraft is an unmanned aerial vehicle. In suchsituations, sensor data is sent via the downlink to the remote pilot andreturn commands are sent to the aircraft via the uplink. Whether thepilot is onboard or remote, in some embodiments, the fuel isolation isconfirmed and initiated by the pilot and the control unit 114 receivesthe command signal to initiate the fuel isolation.

In some embodiments, the control unit 114 is programmed with the logicand decision making functionality to receive the sensor signal 317 andbased on at least this sensor signal, automatically determine that fuelisolation is needed. In such embodiments, the control unit 114 does notneed any signaling from the pilot 318 and initiates the fuel isolationprocess. The control unit 114 may use the sensor signal 317 and othersensor values an determine an engine fire condition exists.

As can be seen in some embodiments, the use of a traditional shut offvalve e.g., shut off valve 108 at or upstream of the firewall 110 is notneeded to provide fuel isolation. It is noted that other shut off valvespresent in the system are not replaced, such as the engine shut offvalve that is at the engine 112. The use of the valve 202, connector 208and air line 210 allows for the replacement of conventional shut offvalves in the fuel feed line 104.

In some embodiments, in the illustrated configuration, the fuelisolation to the firebay 118 is also reversible in the event it isdetermined that the event is not an actual engine fire. In such event,the control unit 114 outputs signals to turn on the fuel pump/s 106 andclose the valve 202, unfeather the propeller/s, and then turn back onthe engine 112. In this case, the flow of fuel will resume to the engineand normal operation will resume after the air in the fuel line passesthrough the engine.

In some embodiments, as described above, the fuel isolation system andmethod does not introduce a single point of failure in the system, asdoes a traditional shut off valve 108. If the valve 202 erroneouslypartially or fully opens due to an electrical and/or mechanical failure,only a small portion of the flowing fuel may pass through the valve 202and reenter the fuel tank 102, and a sufficient amount of fuel toprovide for safe operation of the engine 112 will continue flowingthrough the fuel feed line 104 through the firewall 110 to the engine112. In accordance with some embodiments, in order for catastrophic fuelsystem failure, multiple system components would need to fail.

FIG. 5 comprises a diagram of a system for isolating fuel from thefirebay of an aircraft according to some embodiments. This illustratedembodiment depicts a side elevation view of an example fuel system andin more detail, illustrates the various hoses, pipes, connectors andcomponents of a fuel feed line 504. Illustrated are a header tank 518having an ullage portion 514 and a fuel portion 516. Illustrated is anexample of the various piping, hose and conduit structures that form thefuel feed line 504 that extends from the header tank 518 through thefirewall 522 to the engine 512. For example, on a cold side portion 504a of the fuel feed line, fluid pipe structure connects the header tank518 to the fuel pump assembly 506 (positive displacement with internalbypass) which includes several components such as heat exchangers, fuelfilters, etc. The fuel pump assembly 506 is fluidly connected via a hoseto the jet pump manifold 524 which connects to feed tanks (not shown)and to the connector 508 at a high elevation point corresponding to theullage portion 514. As illustrated, the connector 508 is at the highestpoint in the fuel feed line 504 a, but it is understood that theconnector may be coupled to the fuel feed line at an elevation point ator above the low elevation level of the ullage portion 514, the lowelevation level indicated at line 520. The hose/pipe/connector structurecontinues at a generally descending elevation through a flow meter 526,the firewall 522 and to the engine 512. The elevational arrangement ofthe header tank 518 feeding the fuel pump assembly 506 at a lowelevation then raising to high point (at connector 508 for example), andthen descending to a lower elevation through the flow meter 526, thefirewall 522 and the engine 512 is intentional and assists in creatingsiphon action to assist the fuel pump assembly 506 in moving fuelthrough the fuel feed line 504. The hot side portion 504 b of the fuelfeed line is the portion in the firebay. The connector 508 is alsofluidly connected to the valve 502 which couples the air line 510 backto the ullage portion 514 of the header tank 518.

Operation of the system of FIG. 5 is similar to the embodimentsdescribed in connection with FIGS. 2 and 4. For example, in someembodiments, when fuel isolation is initiated in response to detectionof an engine fire condition, the control unit (not shown in FIG. 5)outputs electrical signals to shut down the engine 512, to turn off thefuel pump assembly 506 and to open the valve 502. This introduces airfrom the ullage portion 514 (which in some embodiments, is underpressure) into the fuel feed line 504 a at the connector 508. The aircauses a siphon break such that fuel cannot be siphoned past thefirewall 522 and since the fuel pumps are off, fuel is no longer beingpumped. Thus, in some embodiments, the only fuel capable of passing thefirewall 522 is the fuel that was present in the fuel feed line 504 fromthe connector 508 to the firewall 522. As described in some embodiments,the control unit may also briefly open the jettison valve (not shown inFIG. 5) to reduce pressure in the fuel system. And in some embodiments,as described above, the fuel isolation technique is reversible since thevalve 502 can be closed and the engine 512 and fuel pump assembly 506can be turned back on in the event the detected engine fire is not anactual engine fire. And, in some embodiments, as described above, thefuel isolation system and method does not introduce a single point offailure in the system. That is, if the valve 502 were to mechanicallyand/or electrically fail and open during normal operation in which thereis not an engine fire, a sufficient amount of fuel will flow through thefeed line 504 a to allow for safe operation of the engine, and only asmall amount of fuel may flow back through the valve and reenter theheader tank 518. It is noted that in some embodiments, the air from theullage portion 514 is under pressure relative to atmospheric pressure.In other embodiments, the air in the ullage portion 514 is not underpressure such that the fuel tank is open to atmospheric pressure, e.g.,when the fuel tank is not full or when the jettison system is activated.Whether the air from the ullage portion 514 is pressurized or not, theopening of the valve 502 introduces air from the ullage portion 514 intothe fuel feed line 504 a at the connector 508.

Referring next to FIG. 6, a flow diagram is shown that illustrates aprocess for isolating fuel from the firebay of an aircraft according tosome embodiments. The process of FIG. 6 may be performed by one or moreof the various systems described herein (such as those described inconnection with FIGS. 2, 4 and 5) and other systems.

A first step is to detect a condition indicative of an engine fire (Step602). In some embodiments, sensors are positioned proximate to theengine in the firebay to detect excessive heat that indicates a possibleengine fire. In some embodiments, a redundant sensor array is providedthat includes a gas that expands to break a pressure switch and anelectrical signal is output to the control unit of the fuel system.

Next, it is determined if fuel isolation is to be initiated (Step 604).As described herein, receipt of a signal from the sensors does notalways mean that there is an actual engine fire. In some embodiments,the control unit transmits a message to the pilot (onboard or remote).The pilot evaluates the warning in view of any other sensed values andfacts and determines whether to initiate fuel isolation. When the pilotintends to initiate fuel isolation, the pilot outputs a command to thecontrol unit to initiate the fuel isolation. In other embodiments, thedecision to initiate fuel isolation is made by the control unit. In suchembodiments, the control unit is programmed with the logic and decisionmaking functionality to evaluate the engine fire sensor signal and othersensor values and factors to automatically determine that fuel isolationis to be initiated. In some embodiments, it is important that a pilot beable to evaluate the facts and make a final determination as to whetherto isolate fuel from the engine. This can be especially important insingle engine aircraft since isolation will result in complete loss ofpropulsion. However, as has been described herein, fuel isolationtechniques of several embodiments are easily reversible to return tonormal flying operation. In such cases, since the risk of catastrophicresults associated with isolating fuel in the event of detected enginefire when there is not an actual engine fire are lower due to thereversibility of the fuel isolation approach of some embodiments, systemdesigners may be more willing to rely on an automated decision by thecontrol unit to initiate fuel isolation. If the decision is to notisolate fuel in Step 604, then the process terminates. Whether the pilotor control unit determines that fuel isolation is needed, the controlunit takes action and outputs control signals to sequence the isolation.

In some embodiments, the control unit is programmed to automaticallydetermine that fuel isolation is to be initiated. In some cases, thismay occur, for example, when a remote piloted aircraft is temporarilyflying ‘lost link’ (i.e., out of communication with the remote pilot).In some cases, the control unit receives signal/s from sensor/sindicating a possible engine fire. Signals from redundant sensor/sassist the control unit in determining whether the sensed engine firecondition should result in fuel isolation. In some embodiments, theengine firebay is fireproof/resistant and can accommodate sustained firefor a period of time (e.g., 5 minutes). Thus, in some embodiments, thecontrol unit delays the determination within the period of time to allowtime for a remote pilot to reconnect to the aerial vehicle. In someembodiments, if the remote pilot does not reconnect within a timethreshold, the control unit makes the determination that fuel isolationis to occur. In such situations, the control unit can make additionalautomatic determinations, such as finding and executing a suitable glidepath based on the flight plan.

When the decision is to isolate fuel from the firebay (Step 604), insome embodiments, the control unit outputs signals to shut down theengine and feather one or more of the propellers (Step 606). In someembodiments, to shut down the engine, the control unit sends a signal toclose the engine fuel shut off valve. Feathering the propellers providesthe lowest drag and gives the aircraft the best glide performance giventhat the engine is being shut down.

Next, power is removed to the fuel pump/s (Step 608) in order to turnoff the fuel pump/s. In some embodiments, the control unit outputscontrol signals to turn off the fuel pumps, and in some cases, thecontrol signal results in power being removed from the fuel pumps. Theturning off of the airframe fuel pumps stops the pumping of fuel fromthe fuel tank through the fuel feed line and firewall to the enginewithin the engine firebay.

At about the same time or slightly after Step 608 is performed, thevalve is opened (Step 610). In some embodiments, the valve (e.g., valve202, 502) is coupled to a connector (e.g., connector 208, 508) coupledinline with the fuel feed line at a location of a cold side portion ofthe fuel feed line (the cold side portion of the fuel feed line extendsfrom the fuel tank to the firewall, the hot side portion of the fuelfeed line extends from the firewall to the engine). In some embodiments,the valve is in a normally closed orientation. The valve also couples anair line (e.g., air line 210, 510) extending from the valve to theullage portion of the fuel tank. In some embodiments, the connector iscoupled inline with the fuel feed line at a high elevation location ofthe cold side of the fuel feed line, the high elevation location at orabove an elevation corresponding to a low elevation level of the ullageportion of the fuel tank. And in some embodiments, the connector iscoupled inline with the fuel feed line at a high elevation pointlocation of the cold side of the fuel feed line. In some embodiments,the connector is a tee connector.

A result of opening the valve in Step 610 is that air from the ullageportion of the fuel tank is introduced via the air line and the valveinto the fuel feed line to provide a siphon break in the fuel line suchthat the fuel cannot be siphoned by the engine, ruptured lines or othercause, and the only fuel reaching the engine is the remaining fuel inthe fuel feed line downstream of the connector and the introduced air.This results in isolation of fuel from the engine firebay without theuse of a traditional shut off valve at or upstream of the firewall.

Next, a jettison valve fluidly connected to the fuel tank is opened(Step 612) and then closed (Step 614) after a period of time. In someembodiments, the period of time is short and for the purpose of ensuringsufficient ullage and/or reducing pressure in the fuel system. That is,in some embodiments the jettison valve is not being opened to jettisonfuel in its normal use. The jettison valve 312 is blipped, i.e., openedfor a short duration, then closed. The duration may be dependent on thecharacteristics of the specific system but in some embodiments, may bebetween about 5 and 30 seconds, between about 10 and 20 seconds. In someembodiments, the jettison valve is opened for about 15 seconds.

At this point in the process, in some embodiments, fuel has beenisolated from the engine firebay such that fuel is not pumped to theengine, and the air introduced creates a siphon break so that fuelcannot be siphoned from the fuel tanks to the engine. Pressure in thefuel system is relieved and the propeller/s are feathered for best glideperformance. Fuel is isolated without use of a shut off valve in thefuel feed line on the cold side of the firewall avoiding a single pointof failure. In the event of a mechanical and/or electrical failure ofthe valve when there is not an engine fire or not a command to initiatefuel isolation, due to the configuration of the piping sizes andarrangement, a sufficient level of fuel continues to flow through thefuel feed line and the connector from the fuel tank to the engine toallow for safe operation of the engine. And in this event, a smallportion of the fuel is diverted through the valve back to the fuel tankvia the air feed line.

Referring next to FIG. 7, a flow diagram is shown that illustrates aprocess for restarting engine operation after fuel has been isolatedfrom the aircraft firebay according to some embodiments. The process ofFIG. 7 may be performed by one or more of the various systems describedherein (such as those described in connection with FIGS. 2, 4 and 5) andother systems. The process of FIG. 7 illustrates the reversibility ofthe fuel isolation techniques described herein.

Initially, it is determined that although fuel isolation was initiated,there has not been an engine fire and fuel isolation is to end (Step702). The control unit then outputs signals to close the valve (Step704) that is functioning as the siphon break in the fuel feed line, andoutputs signals to turn on the fuel pump/s (Step 706). This bringspressure back into the fuel system. Next, signaling is output tounfeather the propeller/s (Step 708). Air movement across the propellercauses the engine to start turning. And next, the engine is turned backon (Step 710). In some embodiments, this signaling causes the enginefuel valve to open which will cause the igniters to come on and theengine will restart normally. As the engine restarts, the air in thefuel feed line will be ingested by the engine and result in a briefreduction in rpm (revolutions per minute) before returning to normaloperation. It is noted that sufficient fuel still remains in the headerfuel tank since the jettison valve was only operated to reduce pressureand not to jettison bulk quantities of fuel in its normal use.

FIG. 8 comprises a functional block diagram of a control unit 802 inaccordance with some embodiments. In some embodiments, the control unitmay be referred to as the engine and fuel interface unit (EFIU). Thecontrol unit 802 may be used as any of the control units describedherein, such as control unit 114. The control unit 802 can beimplemented through one or more processors, microprocessors, centralprocessing unit, logic, local digital storage, firmware and/or othercontrol hardware and/or software, and may be used to execute or assistin executing the steps of the processes, methods and techniquesdescribed herein. In some embodiments, the control module or controlunit 802 includes a control circuit 804, one or more memories 806, oneor more Input/Output (10) interfaces 808 and a bus 810 interconnectingthese components.

In some embodiments, the one or more memories 806 comprisesnon-transitory computer-readable storage mediums storing a set ofcomputer readable instructions. Such memories may comprise volatileand/or non-volatile memory such as such as RAM, ROM, EEPROM, flashmemory and/or other memory technology, and have stored upon it a set ofcomputer readable instructions which, when executed by the controlcircuit 804, causes the control circuit 804 to provide at least thevarious functions described herein.

In some embodiments, the control circuit 804 is a processor-based systemincluding one or more processors. The control circuit 804 and at leastone of the one or more memories 806 may be integrated together, such asin a microcontroller, application specification integrated circuit,field programmable gate array or other such device, or may be separatedevices coupled together. Generally, the control circuit 804 cancomprise a fixed-purpose hard-wired platform or can comprise a partiallyor wholly programmable platform. These architectural options are wellknown and understood in the art and require no further description here.And generally, the control circuit 804 is configured (for example, byusing corresponding programming as will be well understood by thoseskilled in the art) to carry out one or more of the steps, actions,and/or functions described herein.

Typically, the control unit 802 also includes one or more IO interfaces808 such as, ports, connectors, pins, transceivers and the like allowingthe control unit 802 to interface with other circuitry of the aircraft,power supplies and components, communication devices to communicate withother onboard and/or remote systems, other aircraft systems and controlunits, sensors, and so on, and sensors. Communication devices can beconfigured for wired, wireless, optical, fiber optical cable or othersuch communication configurations or combinations of suchcommunications.

Several embodiments describe fuel isolation systems, apparatuses andmethods for use in manned and/or unmanned aerial vehicles (aircraft). Inalternative embodiments, the fuel isolation approaches are applicable inthe same manner in other than aerial vehicles, such as watercraft (e.g.,surface boat or submarine vehicles) and ground vehicles (e.g.,automobiles, trucks). For example, the described approaches andcomponents are applicable in vehicles generally, whether aerial,terrestrial, surface watercraft and submarine watercraft. In someembodiments, the applicability of fuel isolation may be attractive to afuel system designer for vehicles in which loss of life and damage isimminent when fuel is not shut off to the engine or when livingoccupants of the vehicle are not able to easily exit the vehicle in theevent of an engine fire. It is understood that any of the terms usedherein that are specific to aircraft may be more generically named toapply to one or more these other types of vehicles. For example,airframe fuel pumps may be more generically expressed as fuel pumps ormore specifically expressed as a watercraft fuel pumps, an aircraftengine firebay can be more generically expressed as a vehicle enginefirebay or may be more specifically expressed as a watercraft enginefirebay, and so on.

Some embodiments are applicable in single engine and multiple enginevehicles. That is, embodiments of the fuel isolation systems can beapplied to single engine vehicles, such as aircraft. In some cases,these approaches are beneficial in single engine vehicles since atleast: (1) it may be important to reliably shut off fuel to the singleengine in the event of an engine fire condition; (2) fuel isolation isreversible if determined not to be an engine fire; and (3) if the valve(e.g., valve 202, 502) fails, fuel will still flow to the engineallowing for safe operation. In some embodiments using multiple engines,the use of the valve, connector and air line is replicated (paralleled)at the fuel feed line of each engine and controlled by the control unit.If a given engine experiences an engine fire condition, the valve isopened for that engine and not for the others. As such, each engine canhave an independent fuel isolation components controlled by a controlunit. In some embodiments using multiple engines, there is a singleconnection point to the ullage of the header tank, the single connectionpoint coupled to a manifold to variously connect to multiple air linesextending to the valves/connectors of each fuel feed line of eachseparate engine.

It is further noted that in some embodiments, safe operation of the fuelisolation systems, apparatuses and methods is based on breaking thesiphon action in the fuel feed line. Since air is introduced into theline from the ullage of the header tank, in the context of an aerialvehicle, such technique will not operate effectively if the aircraftwere an acrobatic aircraft flying inverted or at steep angles. In suchcases, there may not be an ullage at the connection point to the headertank. However, several embodiments are arranged to be effective givennormal upright aviation (vehicular travel) and normal ascent/descentangles. Such fuel isolation techniques are applicable in various typesof general aviation aircraft, such as cargo aircraft, small commuteraircraft, multi-purpose reconnaissance vehicles, and so on.

Several embodiments of fuel isolation systems, apparatuses and methodsare described herein. In some embodiments, a system and method for usein isolating fuel from an aircraft firebay, the system comprising: afuel tank; an airframe fuel pump; an engine located within the aircraftfirebay; a firewall separating the aircraft firebay from a volumecontaining the fuel tank and the airframe fuel pump; a fuel feed lineextending from the fuel tank to the airframe fuel pump and through thefirewall to the engine, the fuel feed line fluidly connecting the fueltank to the engine and additional aircraft systems, wherein the airframefuel pump is configured to pump fuel from the fuel tank through the fuelfeed line to the engine, wherein the fuel feed line comprises a coldside portion extending from the fuel tank to the firewall and a hot sideportion extending from the firewall to the engine; a connector coupledinline with the fuel feed line at a location of the cold side portion ofthe fuel feed line; a valve coupled to the connector, the valveconfigured in a normally closed orientation; an air feed line coupled toan ullage portion of the fuel tank and to the valve; and a control unitconfigured to control operation of at least the airframe fuel pump andthe valve. In the event of an engine fire, the control unit isconfigured to output control signaling to: turn off the airframe fuelpump to stop pumping the fuel through the fuel feed line; and open thevalve to introduce air from the ullage portion of the fuel tank into thefuel feed line, wherein the air introduced by the valve provides asiphon break in the fuel line such that the fuel cannot be siphoned andthe only fuel that can pass the firewall is the remaining fuel in thefuel feed line downstream of the connector and the introduced air.

In some embodiments, a method for isolating fuel from an aircraftfirebay, the method comprises: in the event of an engine fire, turningoff an airframe fuel pump to stop pumping the fuel through a fuel feedline fluidly connecting a fuel tank to an engine within the aircraftfirebay and passing through a firewall that separates the aircraftfirebay from a volume containing the airframe fuel pump and the fueltank; opening a valve coupled to a connector coupled inline with thefuel feed line at a location of a cold side portion of the fuel feedline, wherein the cold side portion of the fuel feed line extends fromthe fuel tank to the firewall, and wherein a hot side portion of thefuel feed line extends from the firewall to the engine, wherein thevalve is in a normally closed orientation; and introducing, by openingthe valve, air from an ullage portion of the fuel tank into the fuelfeed line to provide a siphon break in the fuel line such that the fuelcannot be siphoned and the only fuel reaching the engine is theremaining fuel in the fuel feed line downstream of the connector and theintroduced air, the air received from an air feed line coupled to theullage portion of the fuel tank and to the valve.

In some embodiments, an apparatus for isolating fuel from an aircraftfirebay comprises: a non-transitory storage medium storing a set ofcomputer readable instructions; and a control unit comprising a controlcircuit configured to execute the set of computer readable instructionswhich causes to the control unit to: output, in the event of an enginefire, control signaling to turn off an airframe fuel pump to stoppumping the fuel through a fuel feed line fluidly connecting a fuel tankto an engine within the aircraft firebay and passing through a firewallthat separates the aircraft firebay from a volume containing theairframe fuel pump and the fuel tank; and output, in the event of theengine fire, control signaling to open a valve coupled to a connectorcoupled in line with the fuel feed line at a location of a cold sideportion of the fuel feed line, wherein the cold side portion of the fuelfeed line extends from the fuel tank to the firewall, and wherein a hotside portion of the fuel feed line extends from the firewall to theengine, wherein the valve is in a normally closed orientation, whereinair from an ullage portion of the fuel tank is introduced into the fuelfeed line to provide a siphon break in the fuel line such that the fuelcannot be siphoned and the only fuel passing the firewall is theremaining fuel in the fuel feed line downstream of the connector and theintroduced air, the air received from an air feed line coupled to theullage portion of the fuel tank and to the valve.

In some embodiments, system for use in isolating fuel from a vehiclefirebay comprises: a fuel tank; a fuel pump; an engine located withinthe vehicle firebay; a firewall separating the vehicle firebay from avolume containing the fuel tank and the fuel pump; a fuel feed lineextending from the fuel tank to the airframe fuel pump and through thefirewall to the engine, the fuel feed line fluidly connecting the fueltank to the engine and additional systems, wherein the fuel pump isconfigured to pump fuel from the fuel tank through the fuel feed line tothe engine, wherein the fuel feed line comprises a cold side portionextending from the fuel tank to the firewall and a hot side portionextending from the firewall to the engine; a connector coupled inlinewith the fuel feed line at a location of the cold side portion of thefuel feed line; a valve coupled to the connector, the valve configuredin a normally closed orientation; an air feed line coupled to an ullageportion of the fuel tank and to the valve; and a control unit configuredto control operation of at least the fuel pump and the valve, wherein inthe event of an engine fire, the control unit is configured to outputcontrol signaling to: turn off the fuel pump to stop pumping the fuelthrough the fuel feed line; and open the valve to introduce air from theullage portion of the fuel tank into the fuel feed line, wherein the airintroduced by the valve provides a siphon break in the fuel line suchthat the fuel cannot be siphoned and the only fuel that can pass thefirewall is the remaining fuel in the fuel feed line downstream of theconnector and the introduced air.

It is noted that in some embodiments, air that is introduced into thefuel feed line 104, 504 a via the valve 202, 502 at connector 208, 508may be more generically provided by an air source. In some embodiments,the air source is the ullage portion 204, 514 of the fuel tank 102, 304,518 as described herein. In some embodiments, the air source is aseparate volume containing air that is coupled to the air line 210. Forexample, in some embodiments, instead of the air line 210 connecting theullage portion 204 of the fuel tank 102 to the valve 202 in FIG. 2, aseparate air source (not shown) would be connected by the air line 210to the valve 202. In some embodiments, the air source maintains the airunder pressure, and in other embodiments, the air source is atatmospheric pressure. In some forms, the air source is a vent boxcoupled to the air line 210. In some embodiments, in the event offailure of the valve 202, 502 such that it is at least partially openwhen there is not an engine fire, the fuel continues to flow at asufficient level through the fuel feed line 104, 504 a and the connector208, 508 from the fuel tank 102, 304, 518 to the engine to allow forsafe operation of the engine. And, in some embodiments, in the event ofthe failure of the valve 202, 502 such that it is at least partiallyopen when there is not an engine fire, a portion of the fuel flowingthrough the fuel feed line is diverted through the valve 202, 502 to thevolume of the air source via the feed line 210. In some embodiments, thefuel returned into the volume of the air source is one or more of:collected in the volume of the air source; dumped/jettisoned from thevolume of the air source to the environment; and returned from thevolume of the air source to the fuel tank 102, 304. It is understoodthat known valves, vents, pipes, hoses, connectors and the like can beused to appropriately route the returned fuel. It is further noted thatin some embodiments, the connector 208, 508 is coupled inline with thefuel feed line 104, 504 a at a high elevation location of the cold sideof the fuel feed line, the high elevation location at or above anelevation corresponding to a low elevation point of the air source ofthe fuel tank 102, 304. For example, similar to that shown in FIG. 2,the connector 208 is coupled to the fuel feed line 104 at or above a lowelevation of the point of the air source, which can be represented atline B.

Accordingly, in some embodiments, a system and method for use inisolating fuel from an aircraft firebay, the system comprising: a fueltank; an airframe fuel pump; an engine located within the aircraftfirebay; a firewall separating the aircraft firebay from a volumecontaining the fuel tank and the airframe fuel pump; a fuel feed lineextending from the fuel tank to the airframe fuel pump and through thefirewall to the engine, the fuel feed line fluidly connecting the fueltank to the engine and additional aircraft systems, wherein the airframefuel pump is configured to pump fuel from the fuel tank through the fuelfeed line to the engine, wherein the fuel feed line comprises a coldside portion extending from the fuel tank to the firewall and a hot sideportion extending from the firewall to the engine; a connector coupledinline with the fuel feed line at a location of the cold side portion ofthe fuel feed line; a valve coupled to the connector, the valveconfigured in a normally closed orientation; an air feed line coupled toan air source and to the valve; and a control unit configured to controloperation of at least the airframe fuel pump and the valve. In the eventof an engine fire, the control unit is configured to output controlsignaling to: turn off the airframe fuel pump to stop pumping the fuelthrough the fuel feed line; and open the valve to introduce air from theair source into the fuel feed line, wherein the air introduced by thevalve provides a siphon break in the fuel line such that the fuel cannotbe siphoned and the only fuel that can pass the firewall is theremaining fuel in the fuel feed line downstream of the connector and theintroduced air. In some embodiments, in the event of a failure of thevalve such that it is at least partially open when there is not anengine fire, the fuel continues to flow at a sufficient level throughthe fuel feed line and the connector from the fuel tank to the engine toallow for safe operation of the engine. And in some embodiments, in theevent of the failure of the valve such that it is at least partiallyopen when there is not an engine fire, a portion of the fuel flowingthrough the fuel feed line is diverted through the valve to the airsource via the air feed line. And in some embodiments, the connector iscoupled inline with the fuel feed line at a high elevation location ofthe cold side of the fuel feed line, the high elevation location at orabove an elevation corresponding to a low elevation point of the airsource.

Those skilled in the art will recognize that a wide variety of othermodifications, alterations, and combinations can also be made withrespect to the above-described embodiments without departing from thescope of the invention, and that such modifications, alterations, andcombinations are to be viewed as being within the ambit of the inventiveconcept.

What is claimed is:
 1. A system for use in isolating fuel from anaircraft firebay, the system comprising: a fuel tank; an airframe fuelpump; an engine located within the aircraft firebay; a firewallseparating the aircraft firebay from a volume containing the fuel tankand the airframe fuel pump; a fuel feed line extending from the fueltank to the airframe fuel pump and through the firewall to the engine,the fuel feed line fluidly connecting the fuel tank to the engine andadditional aircraft systems, wherein the airframe fuel pump isconfigured to pump fuel from the fuel tank through the fuel feed line tothe engine, wherein the fuel feed line comprises a cold side portionextending from the fuel tank to the firewall and a hot side portionextending from the firewall to the engine; a connector coupled inlinewith the fuel feed line at a location of the cold side portion of thefuel feed line; a valve coupled to the connector, the valve configuredin a normally closed orientation; an air feed line coupled to an ullageportion of the fuel tank and to the valve; and a control unit configuredto control operation of at least the airframe fuel pump and the valve,wherein in the event of an engine fire, the control unit is configuredto output control signaling to: turn off the airframe fuel pump to stoppumping the fuel through the fuel feed line; and open the valve tointroduce air from the ullage portion of the fuel tank into the fuelfeed line, wherein the air introduced by the valve provides a siphonbreak in the fuel line such that the fuel cannot be siphoned and theonly fuel that can pass the firewall is the remaining fuel in the fuelfeed line downstream of the connector and the introduced air.
 2. Thesystem of claim 1, wherein the fuel feed line does not include a shutoff valve in the cold side portion of the fuel feed line extending fromthe fuel pump to the firewall.
 3. The system of claim 1, wherein in theevent of the engine fire, the control unit is configured to outputcontrol signaling to turn off the engine.
 4. The system of claim 1,wherein the aircraft further comprises one or more propellers, whereinin the event of the engine fire, the control unit is configured tooutput control signaling to cause the feathering of the one or morepropellers.
 5. The system of claim 1, further comprising a jettisonvalve fluidly connected to the fuel tank, wherein in the event of theengine fire, the control unit is configured to output control signalingto open the jettison valve for a period of time to reduce pressure inthe fuel system.
 6. The system of claim 1, wherein in the event of theengine fire is not an actual engine fire, the control unit is configuredto output control signaling to: start the engine; turn on the airframefuel pump; and close the valve such that the fuel will resume flowing tothe engine.
 7. The system of claim 1, wherein in the event of a failureof the valve such that it is at least partially open when there is notan engine fire, the fuel continues to flow at a sufficient level throughthe fuel feed line and the connector from the fuel tank to the engine toallow for safe operation of the engine.
 8. The system of claim 7,wherein in the event of the failure of the valve such that it is atleast partially open when there is not an engine fire, a portion of thefuel flowing through the fuel feed line is diverted through the valve tothe fuel tank via the air feed line.
 9. The system of claim 1, whereinthe connector is coupled inline with the fuel feed line at a highelevation location of the cold side of the fuel feed line, the highelevation location at or above an elevation corresponding to a lowelevation point of the ullage portion of the fuel tank.
 10. The systemof claim 1, wherein the connector is coupled inline with the fuel feedline at a high elevation point location of the cold side of the fuelfeed line.
 11. The system of claim 1, wherein the connector comprises atee connector coupled inline with the fuel feed line and coupled to thevalve.
 12. The system of claim 1, further comprising one or more sensorsproximate to the engine and configured to detect a condition indicativeof an engine fire and provide sensor signaling to the control unit. 13.The system of claim 12, wherein the control unit is configured to:receive the sensor signaling; transmit a message to a pilot to indicatethe detection of the condition indicative of the engine fire; receive acommand from the pilot to initiate fuel isolation; and output controlsignaling to turn off the airframe fuel pump to stop pumping the fuelthrough the fuel feed line and to open the valve to introduce the airinto the fuel feed line.
 14. The system of claim 12, wherein the controlunit is configured to: receive the sensor signaling; based on at leastthe received sensor signaling, determine that fuel isolation is needed;and output control signaling to turn off the airframe fuel pump to stoppumping the fuel through the fuel feed line and to open the valve tointroduce the air into the fuel feed line.
 15. The system of claim 1,wherein the aircraft comprises one of a manned aerial vehicle and anunmanned aerial vehicle.
 16. The system of claim 1, wherein the aircraftcomprises one of multi-engine aircraft and a single engine aircraft. 17.A method for isolating fuel from an aircraft firebay, the methodcomprising: in the event of an engine fire, turning off an airframe fuelpump to stop pumping the fuel through a fuel feed line fluidlyconnecting a fuel tank to an engine within the aircraft firebay andpassing through a firewall that separates the aircraft firebay from avolume containing the airframe fuel pump and the fuel tank; opening avalve coupled to a connector coupled inline with the fuel feed line at alocation of a cold side portion of the fuel feed line, wherein the coldside portion of the fuel feed line extends from the fuel tank to thefirewall, and wherein a hot side portion of the fuel feed line extendsfrom the firewall to the engine, wherein the valve is in a normallyclosed orientation; and introducing, by opening the valve, air from anullage portion of the fuel tank into the fuel feed line to provide asiphon break in the fuel line such that the fuel cannot be siphoned andthe only fuel reaching the engine is the remaining fuel in the fuel feedline downstream of the connector and the introduced air, the airreceived from an air feed line coupled to the ullage portion of the fueltank and to the valve.
 18. The method of claim 17, wherein the fuel feedline does not include a shut off valve in the cold side portion of thefuel feed line extending from the fuel pump to the firewall.
 19. Themethod of claim 17, further comprising: in the event of the engine fire,outputting, by a control unit, signaling to turn off the airframe fuelpump and to open the valve.
 20. The method of claim 17, wherein in theevent of the engine fire, outputting, by the control unit, controlsignaling to turn off the engine.
 21. The method of claim 17, wherein inthe event of the engine fire, outputting, by the control unit, controlsignals to causing the feathering one or more propellers of theaircraft.
 22. The method of claim 17, further comprising: in the eventof the engine fire, opening a jettison valve fluidly connected to thefuel tank for a period of time to reduce pressure in the fuel system.23. The method of claim 17, wherein in the event of the engine fire isnot an actual engine fire, the method comprises: outputting, by thecontrol unit, control signaling to start the engine, to turn on theairframe fuel pump and to close the valve such that the fuel will resumeflowing to the engine.
 24. The method of claim 17, wherein in the eventof a failure of the valve such that it is at least partially open whenthere is not an engine fire, flowing fuel at a sufficient level throughthe fuel feed line and the connector from the fuel tank to the engine toallow for safe operation of the engine.
 25. The method of claim 24,wherein in the event of the failure of the valve such that it is atleast partially open when there is not an engine fire, diverting aportion of the fuel flowing through the fuel feed line through the valveback to the fuel tank via the air feed line.
 26. The method of claim 17,wherein the connector is coupled inline with the fuel feed line at ahigh elevation location of the cold side of the fuel feed line, the highelevation location at an elevation corresponding to a low elevationpoint of the ullage portion of the fuel tank.
 27. The method of claim17, wherein the connector is coupled inline with the fuel feed line at ahigh elevation point location of the cold side of the fuel feed line.28. The method of claim 17, wherein the connector comprises a teeconnector coupled inline with the fuel feed line and coupled to thevalve.
 29. The method of claim 17, further comprising: detecting, by oneor more sensors proximate to the engine, a condition indicative of anengine fire; and providing sensor signaling to the control unit.
 30. Themethod of claim 29, further comprising: receiving, at the control unit,the sensor signaling; transmitting a message to a pilot to indicate thedetection of the condition indicative of the engine fire; receiving acommand from the pilot to initiate fuel isolation; and outputtingcontrol signaling to initiate the steps of turning off the airframe fuelpump, opening the valve, and introducing the air.
 31. The method ofclaim 29, further comprising: receiving, at the control unit, the sensorsignaling; determining, based on at least the received sensor signaling,that fuel isolation is needed; and outputting control signaling toinitiate the steps of turning off the airframe fuel pump, opening thevalve, and introducing the air.
 32. The method of claim 17, wherein theaircraft comprises one of a manned aerial vehicle and an unmanned aerialvehicle.
 33. The method of claim 17, wherein the aircraft comprises oneof a multi-engine aircraft and a single engine aircraft.
 34. Anapparatus for isolating fuel from an aircraft firebay, the apparatuscomprising: a non-transitory storage medium storing a set of computerreadable instructions; and a control unit comprising a control circuitconfigured to execute the set of computer readable instructions whichcauses to the control unit to: output, in the event of an engine fire,control signaling to turn off an airframe fuel pump to stop pumping thefuel through a fuel feed line fluidly connecting a fuel tank to anengine within the aircraft firebay and passing through a firewall thatseparates the aircraft firebay from a volume containing the airframefuel pump and the fuel tank; and output, in the event of the enginefire, control signaling to open a valve coupled to a connector coupledin line with the fuel feed line at a location of a cold side portion ofthe fuel feed line, wherein the cold side portion of the fuel feed lineextends from the fuel tank to the firewall, and wherein a hot sideportion of the fuel feed line extends from the firewall to the engine,wherein the valve is in a normally closed orientation, wherein air froman ullage portion of the fuel tank is introduced into the fuel feed lineto provide a siphon break in the fuel line such that the fuel cannot besiphoned and the only fuel passing the firewall is the remaining fuel inthe fuel feed line downstream of the connector and the introduced air,the air received from an air feed line coupled to the ullage portion ofthe fuel tank and to the valve.
 35. The apparatus of claim 34, whereinthe control unit is configured to: output, in the event of the enginefire, control signaling to turn off the engine; and output, in the eventof the engine fire, control signaling to cause the feathering one ormore propellers of the aircraft.
 36. A system for use in isolating fuelfrom a vehicle firebay, the system comprising: a fuel tank; a fuel pump;an engine located within the vehicle firebay; a firewall separating thevehicle firebay from a volume containing the fuel tank and the fuelpump; a fuel feed line extending from the fuel tank to the airframe fuelpump and through the firewall to the engine, the fuel feed line fluidlyconnecting the fuel tank to the engine and additional vehicle systems,wherein the fuel pump is configured to pump fuel from the fuel tankthrough the fuel feed line to the engine, wherein the fuel feed linecomprises a cold side portion extending from the fuel tank to thefirewall and a hot side portion extending from the firewall to theengine; a connector coupled inline with the fuel feed line at a locationof the cold side portion of the fuel feed line; a valve coupled to theconnector, the valve configured in a normally closed orientation; an airfeed line coupled to an ullage portion of the fuel tank and to thevalve; and a control unit configured to control operation of at leastthe fuel pump and the valve, wherein in the event of an engine fire, thecontrol unit is configured to output control signaling to: turn off thefuel pump to stop pumping the fuel through the fuel feed line; and openthe valve to introduce air from the ullage portion of the fuel tank intothe fuel feed line, wherein the air introduced by the valve provides asiphon break in the fuel line such that the fuel cannot be siphoned andthe only fuel that can pass the firewall is the remaining fuel in thefuel feed line downstream of the connector and the introduced air.